1. Field of the Invention
The present invention relates to an ignition apparatus of an internal combustion engine that induces current through a primary coil by rotational movement of an ignition power-generating permanent magnet based on rotation of an output shaft of the internal combustion engine, and discontinues the induced current to induce a voltage across a secondary coil, and applies the voltage induced across the second coil to an ignition plug of the internal combustion engine.
2. Description of the Related Art
A known ignition apparatus of an internal combustion engine is a magneto ignition apparatus. The magneto ignition apparatus includes a permanent magnet mounted to an output shaft of an internal combustion engine, and a primary coil disposed near the permanent magnet. Therefore, current is induced in a primary coil by changes of the magnetic field created by rotational movement of the permanent magnet. An electric line connected to the primary coil is provided with a switch that discontinues or cuts off the current through the primary coil periodically at an engine ignition timing. A great change in current, that is, discontinuation of current, induces a high voltage across the secondary coil facing the primary coil. The voltage induced in the secondary coil is applied to an ignition plug of an internal combustion engine, so that the ignition plug produces discharge.
The switch for discontinuing current through the primary coil can be operated by various control devices, for example, a microcomputer. Japanese Patent Application Laid-Open No. HEI 6-307318, as for example, discloses a construction in which a microcomputer detects a current flowing through the primary coil, and determines an ignition timing based on the detected current, and accordingly switches off a transistor switch.
Normally, the microcomputer or the like is driven by an external power source. Therefore, if the external power source fails, it becomes impossible to perform ignition. Furthermore, a failure of the computer itself also makes it impossible to perform ignition.
Therefore, it is necessary to perform the aforementioned switching on and off by using a more reliable hardware circuit while omitting an external power source. In a conventional circuit, therefore, a cam is provided on an output shaft of the engine. The aforementioned switch is formed by a mechanical breaker that is on/off-controlled by the cam.
However, mechanical breakers are likely to be severely damaged by arc discharge and the like, and therefore have relatively short service lives and require many man-hours of check and maintenance.